Mistakes by GPs when fitting contraceptive coils have led to women unexpectedly becoming pregnant and suffering womb damage.

Some problems involving intrauterine devices (IUDs) have led to large payouts to patients in damages, the Medical Defence Union found.

One unidentified woman who suffered a perforated uterus received more than £100,000 in compensation. Another who had a second IUD fitted, because her GP did not realise she already had one, won a similar sum.

The union, which represents doctors accused of malpractice, studied 98 lawsuits involving a coil brought against GPs between 2002 and 2011. Of those, 39 had led to a complication known as uterine perforation, while 16 involved a family doctor failing to remove a coil before inserting another.

In 12 cases, the woman became pregnant after an alleged error with her IUD, while in nine other cases the GP did not detect that the patient was already expecting a child. If a woman is pregnant, the coil has to be removed as soon as possible, regardless of whether the woman wants to continue carrying the child. But removing it can increase the risk of her having a miscarriage.

Eight cases involved the coil migrating outside the uterus and, in three other women, the device had been incorrectly fitted.

The number of cases is very small, given that 127,000 women a year in England have an IUD fitted in a community medical setting, usually a GP's surgery. In 2008-09, a total of about 660,000 women in Britain used one – about 7% of the 9.5m using contraception at that time. Coils, made of plastic and copper, are an increasingly popular alternative to the Pill and condoms because they offer 99% protection against pregnancy and can last up to 10 years. But downsides include a risk of infection, more painful periods and the possibility that they can dislodge.

"Although the number of cases notified to the union in this area is small, the complications that have led to complaints and claims can be serious and so there is no room for complacence," said Dr Natalie Hayes, an MDU medico-legal adviser. Doctors who fit IUDs should always be mindful of potential complications and have proper training, she added.

As a result of the findings, the union will shortly publish an advisory bulletin on its website about fitting IUDs. They stipulate that doctors should always check for pregnancy before fitting them and also check the patient does not already have a coil in place.

Dr Clare Gerada, chair of the Royal College of GPs, said problems such as a perforated uterus were "rare but known Just because someone sues does not necessarily mean the doctor was negligent. IUDs are a safe, effective and reversible contraception that could be more widely promoted," she added

For women, having an IUD fitted "is an extremely intimate procedure", said Rebecca Findlay, of the sexual health charity FPA. "Women should never feel uncomfortable asking their doctor how often they fit IUDs and our advice is to go where they know doctors are well-practised. Women do phone us with concerns before and after having one and, as well as getting properly trained, doctors must make sure they fit them regularly enough to maintain their skills."